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Technetium 1994
ELSEVIER
Coordination Chemistry Reviews 162 ( | 997) 305-318
Technetium 1994 C a t h e r i n e E. H o u s e c r o f t ConCents
I. 2. 3. 4.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Technetium(VII) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Teehnetium(VI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Technetium(V} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.I. O×o complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. Nitrido complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3. Imido complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. Teehnetiuml IV) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. Teehnetium(III) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7. Teehnetium(II) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8. Technetium(I} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9. Dinudear complexes with metal-metal bonds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10. 9~Tc labelfing studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
205 306 306 307 307 310 311 312 312 3!3 314 3!5 316 3t 7
1. Introduction
This review covers the c o o r d i n a t i o n c h e m i s t r y o f technetium, p u b l i s h e d in i994, a n d follows the f o r m a t o f the 1993 survey [1]. T h e literature has been searched using Current Contents a n d the C a m b r i d g e C r y s t a l l o g r a p h i c D a t a Base, i m p l e m e n t e d t h r o u g h the E T H , ZUrich [2]. A l t h o u g h n o t fully comprehensive, this article gives a significant coverage o f papers published, a l t h o u g h o r g a n o m e t a l l i c complexes h a v e been excluded. Medical a p p l i c a t i o n s o f t e c h n e t i u m c h e m i s t r y are n o t covered p e r se, b u t c o m p o u n d s p r e p a r e d a n d studied with the e x p e c t a t i o n o f possible a p p l i c a t i o n s have been ine|uded. C o m p l e x e s are o r g a n i z e d a c c o r d i n g to the f o r m a l o x i d a t i o n state o f the t e c h n e t i u m centre. T e c h n e t i u m ( V ) c h e m i s t r y is d o m i n a t e d by oxo- a n d nitrido-species, a n d here, for c a t e g o r i z a t i o n purposes, the presence o f the T c - - O o r To--= N m o i e t y takes preference over the d o n o r a t o m s in o t h e r ligands. Caution: 9~I'c is a weak f l - ~ m t t e r ( E = 0 . 2 9 2 MeV~ h/2 2.12 x 105 yr). A special issue o f Radiochim. A c t a prefaced by Y o s h i h a r a [3] a n d dealing with the b e h a v i o u r a n d utilization o f t e c h n e t i u m has a p p e a r e d . W i t h i n this issue, Lieser 0010-8545/97/$32.00 © 1997 Elsevier Science S.A. All rights reserved. PH S0010-8545(96 )01332-X
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has addressed the formation of 99Tc in nuclear reactors, and has included discussions of the generation of 99Mo and 99Tc nuclides for medicine, and the entry of 99Tc into the environment [4].
2. Technetium (VII) Gaseous technetium oxide bromides and iodides have been produced in a Knudsen cell at temperatures up to 900°C when solid technetium oxides TcOx are exposed to Br2 or I2 and O2. Mass spectrometry was used to identify the two dominant products as TcO3Br and TcO3I-the iodide is less stable than the bromide. Minor components of the product mixtures were the technetium(VII) compound TcOzBra and technetium(VI) species TcOzBrz [5]. Two papers describe the ferrocenium salt [Cp2Fe][TcO4] (1). It may be prepared by ion-exchange of [CpaFe] + for [H30] + ions in HTcO4 in water. Structural data show that the compound contains isolated cations and anions in the solid state, although fast dynamic electron transfer is observed [6,7].
(1) The extraction, of technetium( VII ) from nitric acid solution using n-octyl (phenyl)N.N-diisobutylcarbamoylmethylphosphine oxide (cmpo) and tributyl phosphate (tbp) in n-dodeeane or deealin has been investigated. By using the mixed empo-tbp system, an enhancement of the technetium extraction was achieved [8]. The transportation of technetium(VII) and rhenium(VII) from feed solutions (pH 0-1.36) to distilled water or 0.5 M NaHCOa solution using a tbp-decalin membrane supported on a microporous PTFE sheet has been studied. Of the two, the sodium hydrogen carbonate solution provided a greater rate of transport, and a pH of 1 proved to be the most suitable. A permeability coefficient of I 1 x 10.4 cm s"1 was determined for technetium(VII) at pH 0.74 with a NaHCO3 strip solution [9].
3. Technetium (VI) The reaction of [NBu4][TcNC14] with bpy leads to the formation of [TcVINC]3(bpy)] if the reaction is carried out in MeCN. In MeOH, the product is
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[TeVNCl(bpy)]z . A mer-eonformation for [TeNC13(bpy)] (2) is suggested by the results of EPR spectroscopy and this has been confirmed by an X-ray diffraction study. The coordination environment is a distorted oetahedron; the Te-N(nitrido) bond distance is I66.9(4) pro, and the Te-N(bpy) bond trans to the nitfido tigand is lengthened (237.1(4) pro) as a result of the trans-effect [10].
(2)
4. Technetium(V) ~.1. Oxo complexes
The electrolytic reduction of pertechnetate in aqueous solution containing cyanide ions leads to the formation of [TcOz(CN)4] 3" as well as [Tc(CN)6] s" [I1]; ~see also section 7). The high-field syntheses of tdakyl ammonium salts of [TcO(SPh)~- from [TeBr3(NPh)(PPh3)2] have been reported. An absorption at 936 em"I in the IR spectrum rbf the product is assigned to the v(Te=O) mode [12]. Further knido complexes from this study are described in section 4.3. The complex [NBu4][TcOCI4] reacts with the diimines 2,3-bis(2-pyridyl)pyrazine (L) and 2,3-bis(2-pyfidyl)quinoxaline (L') in EtOH to give [TcOC12( X)L] (X = C1 or OEt), [C13OTe(~-L)TcOC12(OEt)] and [TcOCI2(X)L'] ( X = C ] or OEt). IR and 1H N M R spectroscopic data are consistent with the coordination of ligand L through one pyrazine and one pyfidine N atom, whereas it is proposed that L' bonds through two pyridine N-donor sites, thereby producing a 7-membered chelate ring [ 13]. Complex formation of ligand H L = ( 3 ) and its ?% and S-alkyl derivatives HL' with technetium(V) has been investigated and products of the type [TeOC1L~] have been isolated and characterized by IH NMR and IR spectroscopies. The figands act as N,S-donors [14]. With the aim of developing potential brain hna~ng agents, Mastrostamatis et aL have studied the reactions of the tigands (4), L, with [9~q'cOC14]-. Coordination of
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N
SH
CS2H SH R = EtS or Et2N (4)
(3)
the tridentate ligands (4) to the [TcO] 3÷ moiety leaves one coordination site vacant; this may be filled by chloride ion as the complexes [TcOLCI] but if L reacts with a technetium(V) gluconate precursor in the presence of 4-methoxythiophenol (HR'), the product is [TcOLR]. The new complexes have been characterized by UV, IR and IH N M R spectroscopies and single crystal X-ray diffraction studies for [TcOLC1] ( R - - E t S ) (5) and [TcOLR'] ( R = E t z N ) . Studies of the biodistribution of these complexes in mice have revealed a high initial brain uptake and from the data it should be possible to design suitable structural modifications to enhance these properties [15]. The 1H and 13C N M R spectra of three of the series of complexes [TcOLCI] and [TcOLR] have been fully assigned [16].
(5) Ligand (6) H2L possesses two amine substituents with different pK~ values. It reacts with [99mTcO4]"in the presence of stannous tartrate to give the technetium(V) complex [TcOL] (7) which has been structurally characterized by X-ray crystallography. In the pH range 9-10 and at 100°C, the reaction proceeds to give [TcOL'] (also structurally characterized) in which L' is the oxidized imine derivative of (6). Intravenous injection into rats shows a significant uptake of the complexes into the brain [ 17]. The preparation and IR spectroscopic and structural characterization of [TcOL] in which L is N , N ' - b i s - l - ( c a r b o x y - 2 - m e r c a p t o e t h y l ) - l , 2 - d i a r a i n o e t h a n e have been reported. In the product, the technetium(V) centre is six-coordinate with a Tc = O bond distance of 165.7(3) pro; the ligand is bound in an N , N ' , S ' , S ' , O - m o d e with the carboxylate oxygen atom sited trans to the oxo group [18]. The Schiff base
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SH
(6)
(7)
complex [TcO{2-OC6H4CMe=NN=C(S)SMe} {Me2C=NN=C(S)SMe}] has been prepared from [TcOCL]" in acetone. Crystallographic characterization of the product confirms the involvement in the coordination sphere of the deprotonated phenolic oxygen atom which is sited trans to the oxo group. This renders one Schiff base tridentate (PC,O , S ) with the second ligand binding in a didentate N , S - m o d e [ 19]. Ligand (8) H6L may coordinate to the [TcO] 3+ m~:~ietyin a triply deprotonated form to generate neutral complexes [TcO(H3L)] in which one carboxyI group is s),n and the other anti with respect to the oxo-group. This complex gives broad 1H NMR spectra at physiologica! pH and, this, coupled with a lack of crystallographic data, means that it has not been possible to completely characterize the complex. In the present study, Marzitli et aL have addressed the problem of the broad NMR spectroscopic signals and have prepared a related complex with a peniciltamine rather than cysteine-based ligand. This reduces the complexity of the observed coupling. From 2D NMR spectroscopic data it has been possible to assign the 1H NMR spectrum of the new complex, and, additionally, crystallographic data have been obtained. The results show that the coordination of the anti-carboxyl group is pH dependent, and the broadening of the spectrum of [TcO(HaL)] at pH 7 has been attributed to the combined effects of the carboxyl coordination and NH proton dissociation - - the deprotonated amine site competes with the carboxyl group as a donor to the metal centre. The solution studies are complemented by molecular mechanics calculations [20]. The reaction of [99TcO4]" and ligand (9) H4L leads to the formation of racNCh H
CO2H
CO2H
H (8)
HO/ N
HOI N (9)
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(no)
[TcO(HL)] (10), a complex that is also produced by treating [99TcO(L')2] where HzL' is ethane-l,2-diol. The product has been characterized by IR, UV-VIS and ~H N M R spectroscopies, HPLC, mass spectrometry and a single crystal X-ray diffraction study. Electrochemical studies have shown that the redox properties of the NOz group are retained upon complex f o l i a t i o n but the couple shifts to a more positive potential. Chiral HPLC has been used to resolve the enantiomers of [TcO(HL)], but racemization occurs rapidly in water (tl/z < 2 rain) [21].
4.2. Nitrido complexes The reaction of the technetium(V) thiourea complex [TcN(tu)4Cl]Cl with Na2[edtaH2] in aqueous solution results in the formation of [{TcN(tu)}a(edta)2]'6H20 (11) - - the first example of a cyclic nitrido-bridged tetrameric technetium complex. The structure has been crystallographically elucidated; the bridges are asymmetrical with Tc-N distances in the ranges 168.1-169.5 (7) and 197.7-200.9(7) pm. Compound (11) is soluble in water and a range of organic solvents (e.g. EtOH, MeCN, CHzClz, dmf) and in the IR spectrum, an absorption at 984 cm "1 is assigned to the v ( T c = N ) mode [22]. The synthesis of the complex [99TcNL] where H2L = (12) from [99TcNC12(PPh2)2] has been described. The product has been characterized by elemental analysis, IR and N M R spectroseopies, conductivity measurements and an X-ray diffraction study. The metal centre is in a pseudo-square-based pyramidal cnvironment with the nitrido ligand occupying the apical site and the ligand adopting an N,N',S,S'-mode. Pertinent bond distances are Tc ~- N = 162.9 ( 7 ), Tc-N = 208.2 (7),
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311
Six hydrate molecules omitted
(I1) 210.1(8), Tc-S=236.39(29), 236.43(22) pro. The eiectrochemical properties of [99TcNL] have also been investigated [23].
MeS
SMe
(12) 4.3. lmido complexes
The imido complex [TcBr3(NPh)(PPh3)2] has been prepared from K[TcO4], PPha, l-acetyl-2-phenylhydrazine and HBr, and in the presence of a tertiary armne and in methanol, it reacts with thiophenol to give [R3NH][TcO(SPh)~]. The chloro complex [TcCI3(NPh)(PPh3)z] reacts with a 4-fold excess of the sterkcally hhtdered 2,3,5,6-tetramethylbenzenethiol (HL) in ~he presence of a proton scavenger to )Setd [Tc(NPh)Lz(PPhz)]. With a 5-fold excess of 2,6-dhnethylbenzenethio! HL' (again with a proton scavenger), the imido complex [Tc(NPh)L~ is produced. [TcC13(NPh)(PPha)z] is treated with P(C6H4SH-2)3 in the p r i c e of a proton sponge, reduction occurs and the product is the technetiurn(III) complex
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[Tc(PPh3){P(C6H4S-2)s}], Infrared and mass spectrometric data are reported, as well as the IH NMR spectrum of [Tc(PPh3){P(C6H4S-2)s}] [12]. Further imido comp!exes are discussed in section 9, and technetium(V) complexes involving diazenido ligands are described along with related technetium(III) species in section 6. 5. Technetium(IV) A new complex containing the anion [TcC]6] 2" has been prepared and structurally characterized-[Cp2Fe]4[H3OMTcClds. The crystal lattice contains isolated cations and anions as figure (13) illustrates [24].
,%. o o~(~~
°~ 0
o ,,o x tlydrogen atoms are omitted.
(13)
6. Technetium(III) A method of preparing mixed ligand fl-diketonate complexes of technetium(Ill) has been detailed. The strategy is a ligand exchange reaction starting from [Tc(acac)2(NCMe)2] + and has been shown to be successful for the ligands such as PhC(O)CH2C(O)Ph, PhC(O)CH2C(O)Me and tBuC(O)CH2C(O)tBu [25]. Treatment of [TcCI(NNR)2(PPh3)2] (R=4-CIC6H4) with Na[MezNCS2] leads to the formation of the complex [Tc(NNR)(S2CNMez)2(PPh3)]. Similar ligand displacements have been carried out using, for example, salenH2 and ligand (14). Using [TcO4] as the precursor, the technetium(V) complexes [TcCI(NNR)2(SzCNMe2)2], [Tc(NNR)2L2]CI for HL=(14), [TcCI(NNR) (bpy)z][BPh4], [TcCI2(NNR)L'(NH3)] for H2L'=(15), and [TcCI(NNR)L"][BPh4] for H2L" ---(16) have been prepared and characterized by IR and tH NMR spectroscopies and elemental analyses; the HPLC retention times of the products have been reported [26].
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Me
O
Me\ /----N Me
~
H
OH
SH
HS
(14)
(16)
HS~
SH
Only the ipso-carbon atoms of the Ph rings are shown
t17)
(18)
The reaction of K[TcO4] with H3L (17) in the presence of PPh3 leads to the formation of the technetium(III) complex [TcL(PPh3] (18), the single crystal structure of which has been determined. The metal centre is in a tfigonal bipyramidal environment with the nitrogen donor and the PPh3 ligand occupying the axial sites. Complex (18) may also be obtained from the reaction of [TcCt3(PPh3)z(NCMe)] with H3L, but in this reaction, a minor product is [TcL(PPh3)2]. Only 1H N M R spectroscopic data are available for this product, proposed to have an octahedral structure [27]. The technetium(tlI) complex [Tc(PPh3){P(C6H4S-2)3}] was mentioned in section 4 [12]. The formation of complexes involving other potentially S,P-donor iigands have also been investigated. The thiolates L-(HL=PhzPCH2CHzSH or Ph2PCH2CH,CH2SH) react with [TcO4]" to yield neutral, diamagnetk:, five-coordinate technetium(III) complexes [TeL2(L=O)]. When HL is 2-Ph2PC6H4SH, the sixcoordinate complex [TcL3] is formed. The crystal structure determhlafion of [TcL2{Ph,P(O)CH2CH2S}] (19) confirms the oxidation of the phosphine group of one ligand and its pendant bonding mode in the complex. All the products have been characterized by elemental analyses, IR, UV-VlS and IH and 31p N M R spectroscopies, mass spectrometry and cyclic voltammetric measurements [28].
7. Technetium (II) When the technetium(Ill) complex [TcC13(PMezPh)3] reacts with an excess of dmpe, reduction occurs and the product is the technetium(Ii) complex [TcCl2(PMe2Ph)a(dmpe)]. A crysta~ structure determination confirms that the coordination sphere is octahedral, and the chloro ligands are mutually trans (Tc-CI=
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(19)
243.1(5)pm). The Tc-P bond distances lie in the range 239.8-243.5(4) pm and the data suggest that there is a decrease in the degree of Tc-P multiple bonding character as the oxidation state of the metal decreases [29]. The electrolytic reduction of pertechnetate in aqueous solution in the presence of zc-acceptor ligands provides a method of preparing technetium complexes for several oxidation states in the presence of cyanide ions, [TcOz(CN)4] 3- and [Tc(CN)d s are formed, and in the presence of 1010-phenanthroline, the teehnetium(II) cation [Tc(phen)3] 2+ is produced [ 11 ].
8. Teehnetium(I) The preparation of [Tc(CN)6] s" was mentioned above. Other technetium(I) complexes reported in 1994 included [TcCl(dppe)] formed by treating [TcC14(PPh3)2] with zinc in the presence of dppe. The complex [TcCl(dppe)] is very air sensitive but is stable under helium or argon atmospheres. Under dinitrogen, it forms [Tc(Nz)Cl(dppe)] but when heated in toluene, this complex loses N: again. With dihydrogen, [TcCl(dppe)] reacts to give [Tc(H2)Cl(dppe)], but again, the uptake of the diatomic molecule is reversible. [Tc(Hz)Cl(dppe)] represents the first example of all t/2-H2 complex of technetium and it has been characterized by tH NMR spectroscopy and crystallography. The H2 ligand lies trans to the chloro group, but the molecule is disordered with respect to these sites [30]. The single crystal structures of trans-[Tc(H20)2(dppe)2][BPh4] (20) [31] and trans-[TcCl(NO){1,2(Me2As)2C6H4}2] (in which the nitrosyl and chloro ligands are disordered) [32] have been determined.
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Only the ipso-carbon atoms of the Ph rings are shown
(20) 9. Dinuclear complexes with metal-metal lmnds The multiply bonded dimers [Tc2C14(PRa)4] have been prepared and characterized for PRs=PEt~, I~Pr3, PMePh2 and PMe2Ph. The synthetic strategy involves the 2-electron chemical reduction of [TcC14(PR3),]. Structural data for [Tc2CI4(PEt3)4], [Tc2C14(PMePh2)a] and TczC14(PMe2Ph)4] show that the molecules possess an eclipsed conformation with D2a symmetry as shown in structure (21). The Tc-Tc bond distances in the three comFounds are 213.3(3) pm (PEt3), 212.7(t) pm (PMe2Ph) and 213.84(5) pm (PMePh2). Taken with the spectro~opic results~ these structural data suggest the presence of Te = Te triple bonds with a 0%~46z~*z electronic configuration in the ground state. Electrochemical studies have shown that each dimer undergoes two reversible one-electron oxidation processes [33].
Tc2Cl4,o# core only (21)
Tc2N6 core only
(22)
The reduction of the imido complex [Tc(NAr)3I ] (Ar = 2,6-Me2C6H4) with sodium results in the formation of the dinuclear compound [Tcz(NAr)4(I~-NAr)~, the core of which is shown in structure (22). When the more sterically hindered
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[Tc(NAr')3I] (Ar'=2,6-iPr2C6Ha) is reduced in a similar reaction, the product is [Tc2(NAr')d which possesses an ethane-like Tc2N 6 core. Both ditechnetium compounds have been crystallographically characterized. Further reduction of [Tcz(NAr')6] leads to cleavage of the metal-metal bond and the formation of [Tc(NAr')3] 3". This anion reacts with HgBr2 to yield the heterometallic species[(Ar'N)3TcHgBr] and [(Ar'N)3TcHgTc(NAr')3], whilst with [Ph3PAuC1], the product is [(Ar'N)3TcAuPPh3]. The structural characteristics of [(Ar'N)3TcAuPPh3] and [(Ar'N)3TcHgTc(NAr')3 ] have been confirmed by the results of X-ray diffraction studies. In the former compound, the Tc-Au bond distance is 258.9( 1) pm and the Tc-Au-P core is, as expected, linear. The Tc,-Hg-Tc core of [(Ar'N)3TcHgTc(NAr')3] is linear with Tc-Hg bond distances of 261.5( 1) pro. Fenske-Hall molecular orbital calculations have been used to analyse the bonding in the model compound Tc2(NH)6 having either an ethane-like or bridged structure [34].
| 0 . 99roTe |abelling studies
This final section reports representative papers dealing with 99mTclabelling studies. A quantitative radio-HPLC method for the analysis of radiolabelled 99mTCcomplexes including proteins and antibodies has been developed by MudduKrishna et al. The strategy is the re-oxidation to [TcO4] of reduced column-absorbed 99mTCspecies; the oxidizing agent in H202. Automation of the procedure has resulted in analysis times of ~ 3 0 min [35]. After reduction of complex-bound 99Tc by tin(II), complex formation with 2,3-dicarboxypropane-l,l-diphosphonic acid leads to the formation of two complexes which are characterized in their electronic spectra by absorptions at 2ma~ 410 nm (pH 3-7) and 2m~x515 nm (pH 5-9.6). The stoichiometries of these complexes have been determined by Job's method to be 2:1 and 2:3, and the oxidation states of the technetium in the complexes have been determined by potentiometric titration - - technetium(Ill) or technetium(IV) is present depending upon the reducing conditions. The results are important within diagnostic nuclear medicine because they address the dependence of 99mTC radiopharmaceutical complexes on the sequence of reagent addition [36]. Hydroxamamide-based ligands may be useful in respect of desigr~ed 99mTc radiopharmaceutical complexes with chelating ligands. Three such ligands have been studied - - benzohydroxamamide, 4-toluhydroxarnamide and 4-pyridylhydroxamamide. Radiolabelling using the stannou~: tartrate method was successful and the resulting 99roTe-labelled complexes were tested for organ distribution, blood clearance and urinary excretion in mice [37]. A 99~nTc-labelled complex containing the bis(oxime) ligand 2,9-bis(hydroxyimino)-4,7-diaza-5,6-dioxodecane has been prepared. Its protein binding, partition coefficient and tissue distribution have been studied, as have those of two related complexes, but the biodistribution is not exceptional [38]. New methods to synthesize derivatives of the ligand 4,8-diaza-3,3,9,9-tetramethylundeca-2,10-dione dioximes h~tve been developed;
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labelled technetium complexes of these tigands are of interest as corranercial radiopharmaceuticals [39]. 99mTc-Labelled complexes containing mercaptacetyltfiglycine and related ligands have been investigated. Both direct labelling and ligand exchanges reactions were monitored using radio-TLC separation. Compounds in which there is a strongly polar sulfonyl substituent exhibit lower protein binding than complexes with mercaptacetyltdglycine, and this characteristic makes the former compounds potentially useful as renal agents [40].
References [l] C.E. Housecroft, Coord. Chem. Rev. 146 Part 2 (1995) 191. [2] F.H. Allen, J.E. Davies, J.J. Galloy, O. Johnson. O. Kennard, C.F. Macrae. E.M. Mitchell, G.F. Mitchell, J.M. Smith, D.G. Watson, J. Chem. Inf. Comp. Sci. 31 (1991) 187. [3] K. Yoshihara, Radiochim. Acta 63 (1993) U4. [4] K.H. Lieser, Radiochim. Acta 63 (1993) 5. [5] J.K. Gibson, Radiochim. Acta 64 (1994) I85. [6] N.A. Baturin, M.S. Gdgoriev, S.V. Kryutchkov, V.G. Makismov. Koord. Khim. 20 (1994) 671. [7] B.G. Antipov, S.V. Kryutchov, V.N. Gerasimov, M.S. Grigofiev, P.E. Kazin, V.V. Khafitonov, V.G. Maksimov, V.S. Moisa, V.V. Sergeev, T.K. Yurik, Radiochim. Acta 64 (1994) 191. [8] M. Takeuchi, S. Tanaka, M. Yamawaki, Radiochim. Acta 63 (1993) 97. [9] S. Ambe, Y. Ohkubo, Y. Kobayashi. M. lwamoto. M. Yanokura, H. Maeda, F. Ambe, Radiochim. Acta 63 (1993) 49. [10] B. Lorenz, P. Kranke, K. Schmidt, R. Kirmse, R. Hubener, U. Abram, Z. Anorg. AUg. Chem. 620 (1994) 921. [11] F. Cerda, C. Kremer, D. Gambino, E. Kremer, J. RadioanaL Nucl. Chem. Lett. 186 (1994)291. [12] T. Nicholson, J. Cook, A. Davison, A.G. Jones, Inorg. Chim. Acta 218 (1994) 97. [13] J.G.H. Dupreez, T.I.A. Gerber, R. Jacobs, J. Coord. Chem. 33 (1994) 147. [14] T.I.A. Gerber, J.G.H. Dupreez, H.J. Kemp, J. Coord. Chem. 33 (1994) 245. [15]S.G. Mastrostamatis, M.S. Papadopoulos, I.C. Pirmettis, E. Paschati, A.D. Varvar/gou, C.I. Stassinopoulou, C.P. Raptopoulou, A. Terzis, E. Chiotellis, J. Meal. Chem. 37 (I994) 3212. [16] C.I. Stassinopoulou, M. Pelecanou, S. Mastrostamatis, E. Chiotellis, Magn. Reson. Chem. 32 (1994) 532. [17] L.C. France~,'-,,,;, Y.Y. Yang, M.-P. Kung, X.X. Zhang, J.J. Billings, Y.-Z. Guo, H.F. Kung, J. Med. Chem. 37 . . . . k, "'~82. [18] 1. Pirmettis, S. Mastrostamatis, M. Papadopoulos, C.P. Raptopoulou, A. Terzis, E. a~iotellis, J. Label. Compound. Radiopharm. 34 ( 19941 817. [19] T.I.A. Gerber, J.G.H. Dupreez, R, Jacobs, B.J.A.M. Vanbrecht, J. Coord, Chem. 31 (1994) 31. [20] L.G. Marzilli, M.G. Banaszczyk, L. Hansen, Z. Kuklenyik, R. Cini, A. Taylor, llaorg. Chem. 33
(1994) 4850. [21] K.E. Linder, Y.-W. Chan, J.E. Cyr, M.F. Malley, D.P. Nowomik, A.D. Nunn, J. Meal. Chem. 37 (1994) 9. [22] J. Baldas, S.F. Colmanet, Z. Ivanov, G.A. Williams, J. Chem. Soc., Chem. Commun., (1994) 2153. [23] G. Cros, H.B. Tahar, D.D. Montauzon, A. Gleizes, Y. Coulais, R. Guimud, E. BeHande, R. Pasqualini, Inorg. Chim. Acta 227 (1994) 25. [3~] M.S. Grigoriev, S.V. Kryutchkov, V.G. Maksh-nov. Y.T. Struchkov, A.I. Yanovsky, Koord. Kh/m. 20 (I994) 870. [25] A. Mutalib, T. Sekine, T. Omofi, K. Yoshihara, J. Radioanal. Nucl. Chem. Art. 178 (1994) 31I. [26] J.R. Dilworth, P. Jobanputra, R.M. Thompson, D.C. Povey, C.M. Archer, J.D. Kelly, J. Chem. Sot., Dalton Trans., (1994) 1251.
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[27] H. Spies, M. (]laser, H.J. Pietzsch, F.E. Hahn, O. KintzeI, T. Lugger, Angew. Chem., Int. Ed. Engl. 33 (1994) 1354. [28] F. Tisato, F. Refosco, (3. Bandoi~, C. Bolzati, A. Moresco, J. Chem. Soc., Dalton Trans., (1994) 1453. [29] F.D. Rochon, R. Melanson, P.C. Ko~ig~ Can. J. Chem. 72 (1994) 2183. [30] A.K. Burrell, J.C. Bryan, (].J. Kubas, J. Am. Chem. Soe. 116 (1994) 1575. [31] R. Hubener, U. Abram, W. Hiller, Acta Crystallogr., Sect. C 50 (1994) 188. [32] H.J. Banbery, T.A. Hamor, Acta Crystallogr., Sect. C 50 (1994) 44. [33] C.L Bums, A.K. Burrell, F.A. Cotton, S.C. Haefner, A.P. Sattelberger, Inorg. Chem. 33 (1994) 2257. [34] A.K. Burrell, D.L. Clark, P.L. Gordon, A.P. Satt~lberger, J.C. Bryan, J. Am. Chem. Soc. 116 (1994) 3813. [35] S.N. Muddukrishna, P. Jorge, W. Machner, T.R. Sykes, A.A. Nouhaim, Appl. Radiat. Isotopes 45 (1994) 1009. [36] N. Vanlicrazumenic, V. Nikolic, D. Veselinovie, J. Radioanal. Nucl. Chem. Art. 173 (1993) 261. [37] M. Nakayama, H. Saigo, A. Koda, K. Ozeki, K. Harada, A. Sue,~, S. Tomiguchi, A. Kojima, M. Hara, R. Nakashima, Y. Ohyama, M. Takahashi, J. Takata, Y. Karube, Appl. Radiat. Isotopes 45 (1994) 735. [38] (I.E. Jackson, M.J. Bryne, H. Fakier, R. Hunter, M. Woudenberg, Appl. Radiat. Isotopes 45 (t994) 581. [39] P. Nanjappan, N. Raju, K. Ramalingam, D.P. Nowotnik, Tetrahedron 50 (1994) 8617. [40] J. Komyei, J. Torko, J. Volford, J. Radioanal. Nucl. Chem. Lett. 186 (1994) 189.
Coordination Chemistry Reviews 162 ( | 997) 305-318
Technetium 1994 C a t h e r i n e E. H o u s e c r o f t ConCents
I. 2. 3. 4.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Technetium(VII) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Teehnetium(VI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Technetium(V} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.I. O×o complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. Nitrido complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3. Imido complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. Teehnetiuml IV) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. Teehnetium(III) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7. Teehnetium(II) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8. Technetium(I} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9. Dinudear complexes with metal-metal bonds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10. 9~Tc labelfing studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
205 306 306 307 307 310 311 312 312 3!3 314 3!5 316 3t 7
1. Introduction
This review covers the c o o r d i n a t i o n c h e m i s t r y o f technetium, p u b l i s h e d in i994, a n d follows the f o r m a t o f the 1993 survey [1]. T h e literature has been searched using Current Contents a n d the C a m b r i d g e C r y s t a l l o g r a p h i c D a t a Base, i m p l e m e n t e d t h r o u g h the E T H , ZUrich [2]. A l t h o u g h n o t fully comprehensive, this article gives a significant coverage o f papers published, a l t h o u g h o r g a n o m e t a l l i c complexes h a v e been excluded. Medical a p p l i c a t i o n s o f t e c h n e t i u m c h e m i s t r y are n o t covered p e r se, b u t c o m p o u n d s p r e p a r e d a n d studied with the e x p e c t a t i o n o f possible a p p l i c a t i o n s have been ine|uded. C o m p l e x e s are o r g a n i z e d a c c o r d i n g to the f o r m a l o x i d a t i o n state o f the t e c h n e t i u m centre. T e c h n e t i u m ( V ) c h e m i s t r y is d o m i n a t e d by oxo- a n d nitrido-species, a n d here, for c a t e g o r i z a t i o n purposes, the presence o f the T c - - O o r To--= N m o i e t y takes preference over the d o n o r a t o m s in o t h e r ligands. Caution: 9~I'c is a weak f l - ~ m t t e r ( E = 0 . 2 9 2 MeV~ h/2 2.12 x 105 yr). A special issue o f Radiochim. A c t a prefaced by Y o s h i h a r a [3] a n d dealing with the b e h a v i o u r a n d utilization o f t e c h n e t i u m has a p p e a r e d . W i t h i n this issue, Lieser 0010-8545/97/$32.00 © 1997 Elsevier Science S.A. All rights reserved. PH S0010-8545(96 )01332-X
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has addressed the formation of 99Tc in nuclear reactors, and has included discussions of the generation of 99Mo and 99Tc nuclides for medicine, and the entry of 99Tc into the environment [4].
2. Technetium (VII) Gaseous technetium oxide bromides and iodides have been produced in a Knudsen cell at temperatures up to 900°C when solid technetium oxides TcOx are exposed to Br2 or I2 and O2. Mass spectrometry was used to identify the two dominant products as TcO3Br and TcO3I-the iodide is less stable than the bromide. Minor components of the product mixtures were the technetium(VII) compound TcOzBra and technetium(VI) species TcOzBrz [5]. Two papers describe the ferrocenium salt [Cp2Fe][TcO4] (1). It may be prepared by ion-exchange of [CpaFe] + for [H30] + ions in HTcO4 in water. Structural data show that the compound contains isolated cations and anions in the solid state, although fast dynamic electron transfer is observed [6,7].
(1) The extraction, of technetium( VII ) from nitric acid solution using n-octyl (phenyl)N.N-diisobutylcarbamoylmethylphosphine oxide (cmpo) and tributyl phosphate (tbp) in n-dodeeane or deealin has been investigated. By using the mixed empo-tbp system, an enhancement of the technetium extraction was achieved [8]. The transportation of technetium(VII) and rhenium(VII) from feed solutions (pH 0-1.36) to distilled water or 0.5 M NaHCOa solution using a tbp-decalin membrane supported on a microporous PTFE sheet has been studied. Of the two, the sodium hydrogen carbonate solution provided a greater rate of transport, and a pH of 1 proved to be the most suitable. A permeability coefficient of I 1 x 10.4 cm s"1 was determined for technetium(VII) at pH 0.74 with a NaHCO3 strip solution [9].
3. Technetium (VI) The reaction of [NBu4][TcNC14] with bpy leads to the formation of [TcVINC]3(bpy)] if the reaction is carried out in MeCN. In MeOH, the product is
C.E. Housecroft / Coordination Chemistry Reviews 162 (1997) 305-318
307
[TeVNCl(bpy)]z . A mer-eonformation for [TeNC13(bpy)] (2) is suggested by the results of EPR spectroscopy and this has been confirmed by an X-ray diffraction study. The coordination environment is a distorted oetahedron; the Te-N(nitrido) bond distance is I66.9(4) pro, and the Te-N(bpy) bond trans to the nitfido tigand is lengthened (237.1(4) pro) as a result of the trans-effect [10].
(2)
4. Technetium(V) ~.1. Oxo complexes
The electrolytic reduction of pertechnetate in aqueous solution containing cyanide ions leads to the formation of [TcOz(CN)4] 3" as well as [Tc(CN)6] s" [I1]; ~see also section 7). The high-field syntheses of tdakyl ammonium salts of [TcO(SPh)~- from [TeBr3(NPh)(PPh3)2] have been reported. An absorption at 936 em"I in the IR spectrum rbf the product is assigned to the v(Te=O) mode [12]. Further knido complexes from this study are described in section 4.3. The complex [NBu4][TcOCI4] reacts with the diimines 2,3-bis(2-pyridyl)pyrazine (L) and 2,3-bis(2-pyfidyl)quinoxaline (L') in EtOH to give [TcOC12( X)L] (X = C1 or OEt), [C13OTe(~-L)TcOC12(OEt)] and [TcOCI2(X)L'] ( X = C ] or OEt). IR and 1H N M R spectroscopic data are consistent with the coordination of ligand L through one pyrazine and one pyfidine N atom, whereas it is proposed that L' bonds through two pyridine N-donor sites, thereby producing a 7-membered chelate ring [ 13]. Complex formation of ligand H L = ( 3 ) and its ?% and S-alkyl derivatives HL' with technetium(V) has been investigated and products of the type [TeOC1L~] have been isolated and characterized by IH NMR and IR spectroscopies. The figands act as N,S-donors [14]. With the aim of developing potential brain hna~ng agents, Mastrostamatis et aL have studied the reactions of the tigands (4), L, with [9~q'cOC14]-. Coordination of
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C.E. Housecrofi / Coordination Chemisto, Reviews 162 :"1997) 305-318 R
N
SH
CS2H SH R = EtS or Et2N (4)
(3)
the tridentate ligands (4) to the [TcO] 3÷ moiety leaves one coordination site vacant; this may be filled by chloride ion as the complexes [TcOLCI] but if L reacts with a technetium(V) gluconate precursor in the presence of 4-methoxythiophenol (HR'), the product is [TcOLR]. The new complexes have been characterized by UV, IR and IH N M R spectroscopies and single crystal X-ray diffraction studies for [TcOLC1] ( R - - E t S ) (5) and [TcOLR'] ( R = E t z N ) . Studies of the biodistribution of these complexes in mice have revealed a high initial brain uptake and from the data it should be possible to design suitable structural modifications to enhance these properties [15]. The 1H and 13C N M R spectra of three of the series of complexes [TcOLCI] and [TcOLR] have been fully assigned [16].
(5) Ligand (6) H2L possesses two amine substituents with different pK~ values. It reacts with [99mTcO4]"in the presence of stannous tartrate to give the technetium(V) complex [TcOL] (7) which has been structurally characterized by X-ray crystallography. In the pH range 9-10 and at 100°C, the reaction proceeds to give [TcOL'] (also structurally characterized) in which L' is the oxidized imine derivative of (6). Intravenous injection into rats shows a significant uptake of the complexes into the brain [ 17]. The preparation and IR spectroscopic and structural characterization of [TcOL] in which L is N , N ' - b i s - l - ( c a r b o x y - 2 - m e r c a p t o e t h y l ) - l , 2 - d i a r a i n o e t h a n e have been reported. In the product, the technetium(V) centre is six-coordinate with a Tc = O bond distance of 165.7(3) pro; the ligand is bound in an N , N ' , S ' , S ' , O - m o d e with the carboxylate oxygen atom sited trans to the oxo group [18]. The Schiff base
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309
SH
(6)
(7)
complex [TcO{2-OC6H4CMe=NN=C(S)SMe} {Me2C=NN=C(S)SMe}] has been prepared from [TcOCL]" in acetone. Crystallographic characterization of the product confirms the involvement in the coordination sphere of the deprotonated phenolic oxygen atom which is sited trans to the oxo group. This renders one Schiff base tridentate (PC,O , S ) with the second ligand binding in a didentate N , S - m o d e [ 19]. Ligand (8) H6L may coordinate to the [TcO] 3+ m~:~ietyin a triply deprotonated form to generate neutral complexes [TcO(H3L)] in which one carboxyI group is s),n and the other anti with respect to the oxo-group. This complex gives broad 1H NMR spectra at physiologica! pH and, this, coupled with a lack of crystallographic data, means that it has not been possible to completely characterize the complex. In the present study, Marzitli et aL have addressed the problem of the broad NMR spectroscopic signals and have prepared a related complex with a peniciltamine rather than cysteine-based ligand. This reduces the complexity of the observed coupling. From 2D NMR spectroscopic data it has been possible to assign the 1H NMR spectrum of the new complex, and, additionally, crystallographic data have been obtained. The results show that the coordination of the anti-carboxyl group is pH dependent, and the broadening of the spectrum of [TcO(HaL)] at pH 7 has been attributed to the combined effects of the carboxyl coordination and NH proton dissociation - - the deprotonated amine site competes with the carboxyl group as a donor to the metal centre. The solution studies are complemented by molecular mechanics calculations [20]. The reaction of [99TcO4]" and ligand (9) H4L leads to the formation of racNCh H
CO2H
CO2H
H (8)
HO/ N
HOI N (9)
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C.E. Houseeroft / Coordination Chemistry Reviews 162 (1997) 305-318
(no)
[TcO(HL)] (10), a complex that is also produced by treating [99TcO(L')2] where HzL' is ethane-l,2-diol. The product has been characterized by IR, UV-VIS and ~H N M R spectroscopies, HPLC, mass spectrometry and a single crystal X-ray diffraction study. Electrochemical studies have shown that the redox properties of the NOz group are retained upon complex f o l i a t i o n but the couple shifts to a more positive potential. Chiral HPLC has been used to resolve the enantiomers of [TcO(HL)], but racemization occurs rapidly in water (tl/z < 2 rain) [21].
4.2. Nitrido complexes The reaction of the technetium(V) thiourea complex [TcN(tu)4Cl]Cl with Na2[edtaH2] in aqueous solution results in the formation of [{TcN(tu)}a(edta)2]'6H20 (11) - - the first example of a cyclic nitrido-bridged tetrameric technetium complex. The structure has been crystallographically elucidated; the bridges are asymmetrical with Tc-N distances in the ranges 168.1-169.5 (7) and 197.7-200.9(7) pm. Compound (11) is soluble in water and a range of organic solvents (e.g. EtOH, MeCN, CHzClz, dmf) and in the IR spectrum, an absorption at 984 cm "1 is assigned to the v ( T c = N ) mode [22]. The synthesis of the complex [99TcNL] where H2L = (12) from [99TcNC12(PPh2)2] has been described. The product has been characterized by elemental analysis, IR and N M R spectroseopies, conductivity measurements and an X-ray diffraction study. The metal centre is in a pseudo-square-based pyramidal cnvironment with the nitrido ligand occupying the apical site and the ligand adopting an N,N',S,S'-mode. Pertinent bond distances are Tc ~- N = 162.9 ( 7 ), Tc-N = 208.2 (7),
C.E. Housecrofi / Coordination Chemistry Reviews 162 (1997) 305-318
311
Six hydrate molecules omitted
(I1) 210.1(8), Tc-S=236.39(29), 236.43(22) pro. The eiectrochemical properties of [99TcNL] have also been investigated [23].
MeS
SMe
(12) 4.3. lmido complexes
The imido complex [TcBr3(NPh)(PPh3)2] has been prepared from K[TcO4], PPha, l-acetyl-2-phenylhydrazine and HBr, and in the presence of a tertiary armne and in methanol, it reacts with thiophenol to give [R3NH][TcO(SPh)~]. The chloro complex [TcCI3(NPh)(PPh3)z] reacts with a 4-fold excess of the sterkcally hhtdered 2,3,5,6-tetramethylbenzenethiol (HL) in ~he presence of a proton scavenger to )Setd [Tc(NPh)Lz(PPhz)]. With a 5-fold excess of 2,6-dhnethylbenzenethio! HL' (again with a proton scavenger), the imido complex [Tc(NPh)L~ is produced. [TcC13(NPh)(PPha)z] is treated with P(C6H4SH-2)3 in the p r i c e of a proton sponge, reduction occurs and the product is the technetiurn(III) complex
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C E. Housecroft / Coordination Chemistry Reviews 162 (1997) 305-318
[Tc(PPh3){P(C6H4S-2)s}], Infrared and mass spectrometric data are reported, as well as the IH NMR spectrum of [Tc(PPh3){P(C6H4S-2)s}] [12]. Further imido comp!exes are discussed in section 9, and technetium(V) complexes involving diazenido ligands are described along with related technetium(III) species in section 6. 5. Technetium(IV) A new complex containing the anion [TcC]6] 2" has been prepared and structurally characterized-[Cp2Fe]4[H3OMTcClds. The crystal lattice contains isolated cations and anions as figure (13) illustrates [24].
,%. o o~(~~
°~ 0
o ,,o x tlydrogen atoms are omitted.
(13)
6. Technetium(III) A method of preparing mixed ligand fl-diketonate complexes of technetium(Ill) has been detailed. The strategy is a ligand exchange reaction starting from [Tc(acac)2(NCMe)2] + and has been shown to be successful for the ligands such as PhC(O)CH2C(O)Ph, PhC(O)CH2C(O)Me and tBuC(O)CH2C(O)tBu [25]. Treatment of [TcCI(NNR)2(PPh3)2] (R=4-CIC6H4) with Na[MezNCS2] leads to the formation of the complex [Tc(NNR)(S2CNMez)2(PPh3)]. Similar ligand displacements have been carried out using, for example, salenH2 and ligand (14). Using [TcO4] as the precursor, the technetium(V) complexes [TcCI(NNR)2(SzCNMe2)2], [Tc(NNR)2L2]CI for HL=(14), [TcCI(NNR) (bpy)z][BPh4], [TcCI2(NNR)L'(NH3)] for H2L'=(15), and [TcCI(NNR)L"][BPh4] for H2L" ---(16) have been prepared and characterized by IR and tH NMR spectroscopies and elemental analyses; the HPLC retention times of the products have been reported [26].
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Me
O
Me\ /----N Me
~
H
OH
SH
HS
(14)
(16)
HS~
SH
Only the ipso-carbon atoms of the Ph rings are shown
t17)
(18)
The reaction of K[TcO4] with H3L (17) in the presence of PPh3 leads to the formation of the technetium(III) complex [TcL(PPh3] (18), the single crystal structure of which has been determined. The metal centre is in a tfigonal bipyramidal environment with the nitrogen donor and the PPh3 ligand occupying the axial sites. Complex (18) may also be obtained from the reaction of [TcCt3(PPh3)z(NCMe)] with H3L, but in this reaction, a minor product is [TcL(PPh3)2]. Only 1H N M R spectroscopic data are available for this product, proposed to have an octahedral structure [27]. The technetium(tlI) complex [Tc(PPh3){P(C6H4S-2)3}] was mentioned in section 4 [12]. The formation of complexes involving other potentially S,P-donor iigands have also been investigated. The thiolates L-(HL=PhzPCH2CHzSH or Ph2PCH2CH,CH2SH) react with [TcO4]" to yield neutral, diamagnetk:, five-coordinate technetium(III) complexes [TeL2(L=O)]. When HL is 2-Ph2PC6H4SH, the sixcoordinate complex [TcL3] is formed. The crystal structure determhlafion of [TcL2{Ph,P(O)CH2CH2S}] (19) confirms the oxidation of the phosphine group of one ligand and its pendant bonding mode in the complex. All the products have been characterized by elemental analyses, IR, UV-VlS and IH and 31p N M R spectroscopies, mass spectrometry and cyclic voltammetric measurements [28].
7. Technetium (II) When the technetium(Ill) complex [TcC13(PMezPh)3] reacts with an excess of dmpe, reduction occurs and the product is the technetium(Ii) complex [TcCl2(PMe2Ph)a(dmpe)]. A crysta~ structure determination confirms that the coordination sphere is octahedral, and the chloro ligands are mutually trans (Tc-CI=
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C.E. Housecroft / Coordination Chemistry Reviews 162 (1997) 305-318
(19)
243.1(5)pm). The Tc-P bond distances lie in the range 239.8-243.5(4) pm and the data suggest that there is a decrease in the degree of Tc-P multiple bonding character as the oxidation state of the metal decreases [29]. The electrolytic reduction of pertechnetate in aqueous solution in the presence of zc-acceptor ligands provides a method of preparing technetium complexes for several oxidation states in the presence of cyanide ions, [TcOz(CN)4] 3- and [Tc(CN)d s are formed, and in the presence of 1010-phenanthroline, the teehnetium(II) cation [Tc(phen)3] 2+ is produced [ 11 ].
8. Teehnetium(I) The preparation of [Tc(CN)6] s" was mentioned above. Other technetium(I) complexes reported in 1994 included [TcCl(dppe)] formed by treating [TcC14(PPh3)2] with zinc in the presence of dppe. The complex [TcCl(dppe)] is very air sensitive but is stable under helium or argon atmospheres. Under dinitrogen, it forms [Tc(Nz)Cl(dppe)] but when heated in toluene, this complex loses N: again. With dihydrogen, [TcCl(dppe)] reacts to give [Tc(H2)Cl(dppe)], but again, the uptake of the diatomic molecule is reversible. [Tc(Hz)Cl(dppe)] represents the first example of all t/2-H2 complex of technetium and it has been characterized by tH NMR spectroscopy and crystallography. The H2 ligand lies trans to the chloro group, but the molecule is disordered with respect to these sites [30]. The single crystal structures of trans-[Tc(H20)2(dppe)2][BPh4] (20) [31] and trans-[TcCl(NO){1,2(Me2As)2C6H4}2] (in which the nitrosyl and chloro ligands are disordered) [32] have been determined.
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Only the ipso-carbon atoms of the Ph rings are shown
(20) 9. Dinuclear complexes with metal-metal lmnds The multiply bonded dimers [Tc2C14(PRa)4] have been prepared and characterized for PRs=PEt~, I~Pr3, PMePh2 and PMe2Ph. The synthetic strategy involves the 2-electron chemical reduction of [TcC14(PR3),]. Structural data for [Tc2CI4(PEt3)4], [Tc2C14(PMePh2)a] and TczC14(PMe2Ph)4] show that the molecules possess an eclipsed conformation with D2a symmetry as shown in structure (21). The Tc-Tc bond distances in the three comFounds are 213.3(3) pm (PEt3), 212.7(t) pm (PMe2Ph) and 213.84(5) pm (PMePh2). Taken with the spectro~opic results~ these structural data suggest the presence of Te = Te triple bonds with a 0%~46z~*z electronic configuration in the ground state. Electrochemical studies have shown that each dimer undergoes two reversible one-electron oxidation processes [33].
Tc2Cl4,o# core only (21)
Tc2N6 core only
(22)
The reduction of the imido complex [Tc(NAr)3I ] (Ar = 2,6-Me2C6H4) with sodium results in the formation of the dinuclear compound [Tcz(NAr)4(I~-NAr)~, the core of which is shown in structure (22). When the more sterically hindered
316
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[Tc(NAr')3I] (Ar'=2,6-iPr2C6Ha) is reduced in a similar reaction, the product is [Tc2(NAr')d which possesses an ethane-like Tc2N 6 core. Both ditechnetium compounds have been crystallographically characterized. Further reduction of [Tcz(NAr')6] leads to cleavage of the metal-metal bond and the formation of [Tc(NAr')3] 3". This anion reacts with HgBr2 to yield the heterometallic species[(Ar'N)3TcHgBr] and [(Ar'N)3TcHgTc(NAr')3], whilst with [Ph3PAuC1], the product is [(Ar'N)3TcAuPPh3]. The structural characteristics of [(Ar'N)3TcAuPPh3] and [(Ar'N)3TcHgTc(NAr')3 ] have been confirmed by the results of X-ray diffraction studies. In the former compound, the Tc-Au bond distance is 258.9( 1) pm and the Tc-Au-P core is, as expected, linear. The Tc,-Hg-Tc core of [(Ar'N)3TcHgTc(NAr')3] is linear with Tc-Hg bond distances of 261.5( 1) pro. Fenske-Hall molecular orbital calculations have been used to analyse the bonding in the model compound Tc2(NH)6 having either an ethane-like or bridged structure [34].
| 0 . 99roTe |abelling studies
This final section reports representative papers dealing with 99mTclabelling studies. A quantitative radio-HPLC method for the analysis of radiolabelled 99mTCcomplexes including proteins and antibodies has been developed by MudduKrishna et al. The strategy is the re-oxidation to [TcO4] of reduced column-absorbed 99mTCspecies; the oxidizing agent in H202. Automation of the procedure has resulted in analysis times of ~ 3 0 min [35]. After reduction of complex-bound 99Tc by tin(II), complex formation with 2,3-dicarboxypropane-l,l-diphosphonic acid leads to the formation of two complexes which are characterized in their electronic spectra by absorptions at 2ma~ 410 nm (pH 3-7) and 2m~x515 nm (pH 5-9.6). The stoichiometries of these complexes have been determined by Job's method to be 2:1 and 2:3, and the oxidation states of the technetium in the complexes have been determined by potentiometric titration - - technetium(Ill) or technetium(IV) is present depending upon the reducing conditions. The results are important within diagnostic nuclear medicine because they address the dependence of 99mTC radiopharmaceutical complexes on the sequence of reagent addition [36]. Hydroxamamide-based ligands may be useful in respect of desigr~ed 99mTc radiopharmaceutical complexes with chelating ligands. Three such ligands have been studied - - benzohydroxamamide, 4-toluhydroxarnamide and 4-pyridylhydroxamamide. Radiolabelling using the stannou~: tartrate method was successful and the resulting 99roTe-labelled complexes were tested for organ distribution, blood clearance and urinary excretion in mice [37]. A 99~nTc-labelled complex containing the bis(oxime) ligand 2,9-bis(hydroxyimino)-4,7-diaza-5,6-dioxodecane has been prepared. Its protein binding, partition coefficient and tissue distribution have been studied, as have those of two related complexes, but the biodistribution is not exceptional [38]. New methods to synthesize derivatives of the ligand 4,8-diaza-3,3,9,9-tetramethylundeca-2,10-dione dioximes h~tve been developed;
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labelled technetium complexes of these tigands are of interest as corranercial radiopharmaceuticals [39]. 99mTc-Labelled complexes containing mercaptacetyltfiglycine and related ligands have been investigated. Both direct labelling and ligand exchanges reactions were monitored using radio-TLC separation. Compounds in which there is a strongly polar sulfonyl substituent exhibit lower protein binding than complexes with mercaptacetyltdglycine, and this characteristic makes the former compounds potentially useful as renal agents [40].
References [l] C.E. Housecroft, Coord. Chem. Rev. 146 Part 2 (1995) 191. [2] F.H. Allen, J.E. Davies, J.J. Galloy, O. Johnson. O. Kennard, C.F. Macrae. E.M. Mitchell, G.F. Mitchell, J.M. Smith, D.G. Watson, J. Chem. Inf. Comp. Sci. 31 (1991) 187. [3] K. Yoshihara, Radiochim. Acta 63 (1993) U4. [4] K.H. Lieser, Radiochim. Acta 63 (1993) 5. [5] J.K. Gibson, Radiochim. Acta 64 (1994) I85. [6] N.A. Baturin, M.S. Gdgoriev, S.V. Kryutchkov, V.G. Makismov. Koord. Khim. 20 (1994) 671. [7] B.G. Antipov, S.V. Kryutchov, V.N. Gerasimov, M.S. Grigofiev, P.E. Kazin, V.V. Khafitonov, V.G. Maksimov, V.S. Moisa, V.V. Sergeev, T.K. Yurik, Radiochim. Acta 64 (1994) 191. [8] M. Takeuchi, S. Tanaka, M. Yamawaki, Radiochim. Acta 63 (1993) 97. [9] S. Ambe, Y. Ohkubo, Y. Kobayashi. M. lwamoto. M. Yanokura, H. Maeda, F. Ambe, Radiochim. Acta 63 (1993) 49. [10] B. Lorenz, P. Kranke, K. Schmidt, R. Kirmse, R. Hubener, U. Abram, Z. Anorg. AUg. Chem. 620 (1994) 921. [11] F. Cerda, C. Kremer, D. Gambino, E. Kremer, J. RadioanaL Nucl. Chem. Lett. 186 (1994)291. [12] T. Nicholson, J. Cook, A. Davison, A.G. Jones, Inorg. Chim. Acta 218 (1994) 97. [13] J.G.H. Dupreez, T.I.A. Gerber, R. Jacobs, J. Coord. Chem. 33 (1994) 147. [14] T.I.A. Gerber, J.G.H. Dupreez, H.J. Kemp, J. Coord. Chem. 33 (1994) 245. [15]S.G. Mastrostamatis, M.S. Papadopoulos, I.C. Pirmettis, E. Paschati, A.D. Varvar/gou, C.I. Stassinopoulou, C.P. Raptopoulou, A. Terzis, E. Chiotellis, J. Meal. Chem. 37 (I994) 3212. [16] C.I. Stassinopoulou, M. Pelecanou, S. Mastrostamatis, E. Chiotellis, Magn. Reson. Chem. 32 (1994) 532. [17] L.C. France~,'-,,,;, Y.Y. Yang, M.-P. Kung, X.X. Zhang, J.J. Billings, Y.-Z. Guo, H.F. Kung, J. Med. Chem. 37 . . . . k, "'~82. [18] 1. Pirmettis, S. Mastrostamatis, M. Papadopoulos, C.P. Raptopoulou, A. Terzis, E. a~iotellis, J. Label. Compound. Radiopharm. 34 ( 19941 817. [19] T.I.A. Gerber, J.G.H. Dupreez, R, Jacobs, B.J.A.M. Vanbrecht, J. Coord, Chem. 31 (1994) 31. [20] L.G. Marzilli, M.G. Banaszczyk, L. Hansen, Z. Kuklenyik, R. Cini, A. Taylor, llaorg. Chem. 33
(1994) 4850. [21] K.E. Linder, Y.-W. Chan, J.E. Cyr, M.F. Malley, D.P. Nowomik, A.D. Nunn, J. Meal. Chem. 37 (1994) 9. [22] J. Baldas, S.F. Colmanet, Z. Ivanov, G.A. Williams, J. Chem. Soc., Chem. Commun., (1994) 2153. [23] G. Cros, H.B. Tahar, D.D. Montauzon, A. Gleizes, Y. Coulais, R. Guimud, E. BeHande, R. Pasqualini, Inorg. Chim. Acta 227 (1994) 25. [3~] M.S. Grigoriev, S.V. Kryutchkov, V.G. Maksh-nov. Y.T. Struchkov, A.I. Yanovsky, Koord. Kh/m. 20 (I994) 870. [25] A. Mutalib, T. Sekine, T. Omofi, K. Yoshihara, J. Radioanal. Nucl. Chem. Art. 178 (1994) 31I. [26] J.R. Dilworth, P. Jobanputra, R.M. Thompson, D.C. Povey, C.M. Archer, J.D. Kelly, J. Chem. Sot., Dalton Trans., (1994) 1251.
318
CE. Housecroft / Coordination Chemistry Reviews 162 (1997) 305-318
[27] H. Spies, M. (]laser, H.J. Pietzsch, F.E. Hahn, O. KintzeI, T. Lugger, Angew. Chem., Int. Ed. Engl. 33 (1994) 1354. [28] F. Tisato, F. Refosco, (3. Bandoi~, C. Bolzati, A. Moresco, J. Chem. Soc., Dalton Trans., (1994) 1453. [29] F.D. Rochon, R. Melanson, P.C. Ko~ig~ Can. J. Chem. 72 (1994) 2183. [30] A.K. Burrell, J.C. Bryan, (].J. Kubas, J. Am. Chem. Soe. 116 (1994) 1575. [31] R. Hubener, U. Abram, W. Hiller, Acta Crystallogr., Sect. C 50 (1994) 188. [32] H.J. Banbery, T.A. Hamor, Acta Crystallogr., Sect. C 50 (1994) 44. [33] C.L Bums, A.K. Burrell, F.A. Cotton, S.C. Haefner, A.P. Sattelberger, Inorg. Chem. 33 (1994) 2257. [34] A.K. Burrell, D.L. Clark, P.L. Gordon, A.P. Satt~lberger, J.C. Bryan, J. Am. Chem. Soc. 116 (1994) 3813. [35] S.N. Muddukrishna, P. Jorge, W. Machner, T.R. Sykes, A.A. Nouhaim, Appl. Radiat. Isotopes 45 (1994) 1009. [36] N. Vanlicrazumenic, V. Nikolic, D. Veselinovie, J. Radioanal. Nucl. Chem. Art. 173 (1993) 261. [37] M. Nakayama, H. Saigo, A. Koda, K. Ozeki, K. Harada, A. Sue,~, S. Tomiguchi, A. Kojima, M. Hara, R. Nakashima, Y. Ohyama, M. Takahashi, J. Takata, Y. Karube, Appl. Radiat. Isotopes 45 (1994) 735. [38] (I.E. Jackson, M.J. Bryne, H. Fakier, R. Hunter, M. Woudenberg, Appl. Radiat. Isotopes 45 (t994) 581. [39] P. Nanjappan, N. Raju, K. Ramalingam, D.P. Nowotnik, Tetrahedron 50 (1994) 8617. [40] J. Komyei, J. Torko, J. Volford, J. Radioanal. Nucl. Chem. Lett. 186 (1994) 189.